Recovery of pure beta-picoline



Patented June 15, 1948 UNITED STATES PATENT OFFICE 2,443,479 v vRECOVERY OF PURE BETA-PICOLINE George Riethof, Mount Lebanon, Pa.,assignor to Pittsburgh Coke & Chemical Company, a corporation ofPennsylvania No Drawing. Application August 20, 1942, 7 Serial No.455,477

7 Claims.v (Cl. 260 -290) This invention relates to the recovery of purebeta-pi-coline; and itis particularly concerned with the methodofrecovcring beta-.picoline substantially free from gamma-picoline andother basic oils, from mixtures of basic oils containing beta andgamma-picoline, said process comprising heating said mixture of basicoils with phihalic anhydride in the presence of acetic anhydride untilthe basic oil other than eta-picoli e, have c ndensed with said phthalican y r de l a in the beta-choline unchan d, and separa lnss cond ns tionp duc from e. nc m n beta-picoline; a d it urt er comp is sa r c wh re nthe basic oil mixturev s prel minarily treated to ef ec emoval. 0.'2.,6-1. l idi y r ctice the 2,6-luticline with ureaa d sepa tin t ereaction produilt irom the basic oil mixture, whereby substantialeconomy of phthalic anhydride may be effected in the subsequent-recoveryof beta-picoline; and it further comprises a procass f p du ng pyr phthne by d n i meth l-sub tut d pyridine o h r t an bet picoline, withphthalic anhydride in the presence of a c an y e; a l as more u ly e inf er set forth and as claimed.

On Of h ncipal nat ral sour s f betapicoline is the basic coal tar oilsin which it oc s n dmixture with its isom rs alphaand gamma-picnics andi s homo og es he lut din Th se, basi ls an cuts rich in beta-picoline,but it is not practicable by simple stillati n to eparate e-tanl ollfrom gannna-pilcoline and from 2,6-'l utidine because all three of thesebasic oils boil at about 142 C. The. p o u old comm rc al y a chn cabeta-picoline often contains fifty per cent or more of other basic oils,being perhaps seventy per cent betaand gamma-choline and the remaindermainly 2,6 -lutidine.

Pure beta-pico-line is not available commercially although beta-picolineof suflicient purity to produce, on oxidation, nicotinic acid having amelting pointof about 232 C. is, in demand for the pr du tion ofnicotinic ac d a d n ot nic acid compounds for fortifyingthe vitamincontent of foods. vThe specification of the melting point of thenicotinic acid formed on oxidation ofbetapicoline is a valuable andaccurate measure of the quality 01 beta-picoline, because it has beenfound that gamma-picoline, when present even very small amounts in thebeta-picoline, will l depress the melting point of the oxidation prodnotto 215 C., or less. Thus. b selection of betapico in which on xida i nyi ld nic in i having a melting point of 232 c. or hi her, a

be fractionated to produce 'picoline and 2,6-lutidine.

2 l high purity, 1 d particularly a matematerial of [of gammarialsubstantially completely free picoline, is assured.

It is an object achieved by the present invention to provide a processwhereby beta-picoline "of such purity that on oxidation it will producenicotinic acid having a melting point above about 232 C. and as high as235 to 237 C. may be recovered from mixtures of beta-pi'coline withother basic coal tar oils, particularly gamma- By the term purebeta-picoline, as used herein and in the appended claims, I lineanbeta-picoline which on oxidation yields nicotinic acid having a meltingpoint of at least 232 C;

I have discovered that when the reaction between a methyl-substitutedpyridine in the methyl group is in the alpha or gamma position withphthalic anhydride in the presence of acetic anhydride, is carried outin the presence of a tertiary amine which does not react with phthalicanhydride, the amine acts to catalyze the reaction so that thecondensation of the alpha or gamma methyl substituted pyridine with thephthalic anhydride proceeds to coinpletion and all, or substantiallyall, of the alpha or gamma methyl-substituted pyridine present isconverted'to a pyro-phthalone. By application of this discovery to basiccoal tar oils, 1 have found that a pure beta-picoline can be recoveredfrom such oils containing beta-pico-line in admixture with alpha orgamma-picoline, or both, and with 2,6-1utidine.

I have found that on heating a mixture of basic coal tar oils containingbeta-picoline, particularly a mixture of beta-picoline withgammapi-coline, or 2,6-lut-idine, or both, with phthalic anhydride inthe presence of acetic anhydride, the beta-picoline, a tertiary aminewhichdoes not react with phthalic anhydr-ide, acts as a catalyst and areaction can be effected between the phthalic anhydride and all of thegamma-picoline, as well as with substantially all Of the 2,6-1utidine,to form compo 7 ds such as the pyrophthalones while the beta-picolineremains unchanged. The r from [these reaction products by distillation.By this process substantially complete separation of the beta-picolinefrom gamma-pico-line and 2,6-lutidine, can be efiected, and thebeta-picoline recovered is of suihciently high purity to produce onoxidation nicotinic acid having a melting point above about 232 0.,usually between 235 and 237 0.

In carrying out the process of my invention beta-picoline is readilyseparable when beta-picoline is to be recovered from a mixture of basictar oils containing relatively large amounts of 2,6-1utidine, it isoften desirable to effect a preliminary separation of 2,6-lutidine.While my process is eifective to recover pure beta-picoline fromadmixture with 2,6-lutidine, it is sometimes more economical to effect apreliminary separation of some of the 2,6-lutidine. Also, a purebeta'picoline can be recovered in somewhat better yield by my processfrom a mixture containing a relatively small amount of 2,6- lutidinethan from one containing a relatively large amount.

Such preliminary separation of 2 ,6-lutidine can be effected by theprocess of my copending United States patent application Serial No.404,932, filed July 31, 1941, now Patent No. 2,295,606, issued September15, 1942. The method therein described comprises treating a mixture ofbasic tar oils containing 2,6-1utidine with urea. The urea reacts withthe 2,6-lutidine to form a crystalline compound which separates out ofthe solution. A mixture of betaand gamma-picoline thus separated from2,6-lutidine may ad.- vantageously be treated according to the presentinvention for the recovery of pure betapicoline.

The process of my invention is usually carried out by mixing the crudebasic oil mixture containing the beta-picoline to be recovered with anamount of acetic anhydride and phthalic an hydride, each equal to orslightly greater than the theoretical amount required to combine withall of the gamma-picoline and 2,6-lutidine present in the crude basicoil mixture. Somewhat smaller amounts of phthalic anhydride may be usedif desired. The mixture of basic oils, acetic anhydride and phthalicanhydride, is heated to a temperature between 130 and 200 C.,advantageously between 160 and 180 C. for a time sufiicient to effectsubstantially complete reac tion between the gamma picoline and the 2,6-lutidine present with the phthalic anhydride. For this purpose I havefound that by heating at a temperature of about 170 C. for about 5 hoursis usually adequate.

As the reaction proceeds a dark oil is formed containing unchangedbeta-picoline and the reaction products and excess reagents. Upondistillation of this oil, beta-picoline mixed with acetic acid can beseparated. This mixture may be neutralized with caustic soda and againdistilled to separate the beta-picoline from the acetic acid. In suchcase, the acetic acid is not recovered. It is usually preferabletherefore to treat this mixture with sulfuric acid to convert thebeta-picoline to its acid sulfate and distill out and recover the aceticacid. The remaining betapicoline acid sulfate upon neutralization, forexample, with caustic soda and re-distillation and drying, yields a purebeta-picoline completely free of gamma-picoline and free orsubstantially free of 2,6-lutidine. The pure beta-picoline thusrecovered upon oxidation yields nicotinic acid having a melting pointabove about 236 C., usu ally 235 to 237 C.

The following example illustrates the results obtained by a method of myinvention:

In this example pure beta-picoline was recovered from a mixture of basictar oils containing about 40 per cent by weight of beta-picoline, 45 percent by weight of gamma-picoline and 15 per cent by weight of2,6-1utidine. This basic oil mixture was obtained by treating a crudecommercial picoline cut with urea, according to the process of mycopending application Serial No. 404,932, to effect a preliminaryseparation of a part of the 2,6-1utidine.

To 800 parts by weight of the picoline mixture there were added 460parts by weight of phthalic anhydride, 300 parts by weight of aceticanhydride. .The mixture was heated to and maintained at 170 to C. for 5hours until the reaction was substantially complete. The reactionmixture was then distilled off to a temperature of 155 C. The distillatewas then neutralized with excess caustic soda and the pure betapicolinewas distilled ofi. The sample of the betapicoline thus recovered wasoxidized to nicotinic acid by the method described by Pinner inBerichte, vol. 33, page 1226 (1900), with the exception that thenicotinic acid was not purifled but was tested in the form in which itcrystallized from the aqueous solution. The resulting nicotinic acid hada melting point of 236 to 237.4" C.

While my invention has been defined herein with respect to certainspecific embodiments thereof, it is to be understood that it is notlimited to such embodiments or details thereof, except as hereinafterdefined in the appended claims.

What I claim is:

1. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picoline, comprisingcombining gamma-picoline with phthalic anhydride by heating the basicoil mixture with said phthalic anhydride at a temperature of 130 to 200C., in the presence of acetic anhydride, and thereafter separating theunchanged betapicoline from the reaction mixture.

2. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picoline and 2,6-lutidine, comprising combining the gamma picoline and 2,6-lutidine withphthalic anhydride by heating the basic oil mixture with said phthalicanhydride at a temperature of 130 to 200 C. in the presence of aceticanhydride, and thereafter separating unchanged beta-picoline from thereaction mixture.

3. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picoline and 2,6-lutidine comprising combining the gamma-picoline and 2,6-lutidine withphthalic anhydride by heating the basic oil mixture with said phthalicanhydride at a temperature of 130 to 200 C. in the presence of aceticanhydride, and thereafter distilling off unchanged beta-picoline fromthe reaction mixture.

4. A process of recovering pure beta-picoline from mixtures of basicoils containing appreciable amounts of beta and gamma-picoline and 2,6-lutidine, comprising reacting the 2,6-lutidine with urea and separatingthe crystalline compound thus formed from the remaining basic oils,combining the gamma-picoline and any remaining 2,6-lutidine withphthalic anhydride by heating the remaining basic oils with phthalicanhydride in the presence of acetic anhydride at a temperature of 130 to200 C. and thereafter distilling off the unchanged beta-picoline fromthe reaction mixture.

5. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picolines and 2,6-lutidine, comprising combining gamma-picoline and 2 ,fi-lutidine withphthalic anhydride by heating the basic oil mixture with said phthalicanhydride at a temperature of 160 to 180 C. in the presence of aceticanhydride and thereafter distilling off the unchanged beta-picoline fromthe reaction mixture.

6. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picoline and 2,6-lutidine, comprising combining the gamma-p100- line and 2,6-1utidinewith phthalic anhydride by heating the basic oil mixture with saidphthalic anhydride at a temperature of 160 to 100 C. in the presence ofacetic anhydride and thereafter distilling off the unchangedbeta-piccline and acetic acid, treating the distillate with sufficientsulfuric acid to convert the beta-picoline to its acid sulfate,distilling oii acetic acid and other impurities from the solution ofbetapicoline acid sulfate, neutralizing the remaining solution withalkali and distilling off and recovering pure beta-picoline.

7. A process of recovering pure beta-picoline from basic oil mixturescontaining appreciable amounts of beta and gamma-picoline and 2,6-lutidine, comprising combining the gamma-picc- REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Riethof Sept. 15, 1942 OTHER REFERENCESBerichte de Deut. Gesell., vol. 32; pp. 1889 and 2526-7; ibid., vol. 21;pp. 1007-10.

J. Chem. Soc. 1933; pp. 77-79.

Maier: DasPyridin und seine Derivate, pp. 31, 32, 35, 46-49, 54 and 59.

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